1. Field of Invention
The present invention relates to an image processing circuit and method. More particularly, the present invention relates to an image processing circuit and method that can scale and sharpen images.
2. Description of Related Art
The advancements in the manufacturing process have made high resolution monitors become more and more popular. High resolution monitors can display more image details clearly. Taking a monitor compatible with the High Definition Multimedia Interface (HDMI) standard, the monitor can display images with a 1920×1080 resolution. Those images with the resolution of 1920×1080 are frequently referred to as High Definition (HD) images.
However, most TV programs can only provide images with a resolution of 320×240. Similarly, DVD programs can only provide images with a resolution of 720×480, which is referred to as Stand Definition (SD). When a monitor having a high resolution (e.g. HD) is used to display a TV program or a DVD program, the monitor has to enlarge the images of the program. Because the enlarged images will have relatively obscure object borders, observers will discern deteriorations in the quality of the enlarged images. Therefore, image sharpening is usually performed upon the enlarged images to enhance the sharpness of the enlarged images.
Please refer to FIG. 1, which is a block diagram of an image processing circuit 10 of the related art. The image processing circuit 10 is used to enlarge and sharpen an input image IIN to generate a sharpened image IS. The image processing circuit 10 includes a scaling circuit 12 and a sharpness circuit 14. The scaling circuit 12 enlarges the input image IIN to generate an enlarged image IP. Then, the sharpness circuit 14 sharpens the enlarged image IP to generate the sharpened image IS.
For simplicity of illustration, when this text indicates that an image has a resolution of U×V, it means that the horizontal resolution of the image is U pixels, and the vertical resolution of the image is V pixels. For example, assume that the resolution of the input image IIN is 720×480. The horizontal resolution of the input image IIN is 720 pixels, and the vertical resolution of the input image IIN is 480 pixels. Please note that each of the aforementioned pixels can consist of either a single sub-pixel or a plurality of sub-pixels. Each of the sub-pixels represents a specific color, such as red, green, or blue.
Please refer to FIG. 2, which is a diagram illustrating the input image IIN, the enlarged image IP, and the sharpened image IS of FIG. 1. Assume that the input image IIN with the resolution of 720×480 is to be converted into the sharpened image IS with the resolution of 1920×1080. The scaling circuit 12 first enlarges the input image IIN to generate the enlarged image IP with the resolution of 1920×1080. Next, the sharpness circuit 14 sharpens the enlarged image IP to generate the sharpened image IS with the resolution of 1920×1080.
When the resolution of the sharpened image IS increases, to maintain the quality of the sharpened image IS, the sharpness circuit 14 must have more taps. However, if the sharpness circuit 14 has more taps, the line buffers 18 must also have larger storage capacities. For example, assume that (1) the input image IIN with the resolution of 720×480 is to be converted into the sharpened image IS with the resolution of 1920×1080; (2) the sharpness circuit 14 performs a 7-tap sharpening; (3) each pixel has three sub-pixels corresponding to colors red, green, and blue; and (4) each sub-pixel has 256 (i.e. 28) gray levels. To facilitate the 7-tap sharpening, the image processing circuit 10 should have at least 6 line buffers 18, each of which should be capable of storing at least 5760 (i.e. 1920×3) bytes.